1. Field of the Invention
The present invention relates to nulling systems adapted to separate desired received data link signals from interference signals and/or jamming signals. More specifically, the present invention relates to right hand and left hand circular polarized electric field vectors or components and to a method of eliminating interference signals sensed at the receiver of the data link.
2. Description of the Prior Art
Heretofore, data link systems have been made which employ linear polarization (LP); right hand circular polarization (RHCP); and left hand circular polzrization (LHCP) of the polarized electric field vectors.
The problem with employing linear polarization in an air to ground or ground to air data link is that the polarization of the received signals are dependent on the orientation of the antenna at the aircraft transmitter, and when the antenna is rotated with maneuvers of the aircraft, the orientation of the electric field vector is also changed and may become cross-polarized with the orientation of the receiving antenna at the ground station so that no signal or an attenuated signal is received. For this reason, data links employing aircraft have tended to employ right hand or left hand circular polarization at the antennas.
A typical prior art example is found in U.S. Pat. No. 4,051,474 which teaches an array of eight transmitting and receiving antennas which are adapted for radar use. The dipole antenna array polarization can be adjusted to be orthogonal to the polarization of a single interference signal in the main beam. The problem with this nulling system is that the system can only be set to overcome one interference signal of unique orientation and does not deal with interference arising in the side lobes or back lobes or dynamic interference signals.
In my copending application Ser. No. 874,448, filed 2 Feb. 1978, a polarization nulling system is taught which is capable of dealing with a single polarization interference signal at a time and only interference signals that are in the main lobe of the antenna radiation pattern.
It would be extremely desirable to provide a nulling system that deals with interference arising in the main lobe as well as the side lobes or back lobes and is also capable of dealing with more than one interference signal of different polarizations at the same time.